A physical quantity PP is related to four observables a,b,ca, b, c and dd as follows: P=a3b2cdP = \frac{a^3 b^2}{\sqrt{c} d}. The percentage errors of measurement in a,b,ca, b, c and dd are 1%1\%, 3%3\%, 4%4\% and 2%2\% respectively. What is the percentage error in the quantity PP?

Model Answer & Options

Source: Extra Practice

13%

7%

10%

14%

Explanation

The relative error in PP is given by the sum of the relative errors of its components multiplied by their respective powers: ΔPP=3Δaa+2Δbb+12Δcc+Δdd\frac{\Delta P}{P} = 3\frac{\Delta a}{a} + 2\frac{\Delta b}{b} + \frac{1}{2}\frac{\Delta c}{c} + \frac{\Delta d}{d}. Substituting the given percentage errors: Percentage error in P=(3×1%)+(2×3%)+(0.5×4%)+(1×2%)=3%+6%+2%+2%=13%P = (3 \times 1\%) + (2 \times 3\%) + (0.5 \times 4\%) + (1 \times 2\%) = 3\% + 6\% + 2\% + 2\% = 13\%. Note that errors are always added to find the maximum possible error, even if the variable is in the denominator.

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